The ASE 15 stored procedure sp_tables doesn’t work with SQL UDFs. sp_tables has the udfs coming back as system tables.
repro:
1) create a sql udf in a db
2) run sp_tables, you will see the UDF as a “SYSTEM TABLE”
DBADEV1.sybase_dba.1> sp_tables;
table_qualifier table_owner table_name table_type remarks
--------------- ----------- ---------- ---------- -------
sybase_dba dbo DATE_FORMAT SYSTEM TABLE NULL
In the above example, the DATE_FORMAT UDF is the one at Porting MySQL’s date_format function to Sybase ASE 15.0.2
I’ve opened a case with Sybase to get this fixed – I’ll post the CR # when I get it.
UPDATE: Sybase assigned CR 497173 to this 
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Well, a few years later and sp_tables is still broken in ASE 15.5
I’ve opened a case with Sybase TechSupport for status and a time frame we can expect this simple fix.